Hot-galvanized carbon-steel alternating-current conductor



May 19, 1942.

F. F. FowLE TAL 2,283,868 HoT-GALvANI'zED CARBON-STEEL ALTERNATING-CURRENT vCONDUCTOR original Filed May 1J, 1938 Patented May 19, 1942 so STATES l F i@y HOT-,GALVANIZED CARBON-STEEL ALTR- NATING-CURRENT CONDUCTOR of Indiana original application May 11, 1988, sei-iai No. 207,351. Divided and this application February 13, 1989, seria1N0.256,112

5 Claims.

Our invention relates to hot-galvanized carbon-steel alternating-current conductors.

This present application is directed to the product. The process for making that product is set forth in our copending application Serial No. 207,351, Iiled May 11, 1938; and the present application is a division of that co-pending application Serial No. 207,351, led as a division in response to a requirement by the Patent Oflice.

The object of our invention is to produce a carbon-steel conductor which is of a type suitable for overhead alternating-current transmission lines and which has an adherent hot-galvanized zinc coating. The term alternating curren is used to include pulsating current.

The carbon-steel alternating-current conductor contemplated by the present application, for use in an overhead electricl transmission line, is of hypo-eutectoid steel which. contains at least 0.25% of carbon, not in excess of 0.30% of manganese, and silicon and phosphorus in suicient amount to make a combined total of at least 0.05% but with the silicon not above 0.25%

and desirably not above,0.15% and with the silicon and phosphorus in sulcient amount to make a combined total of at least 0.05% but with the silicon not above 0.25% and desirablynot above 0.15% and with the phosphorus not above 0.12%, sulfur low although not necessarily absent, and some copper present if it is desired to have a copper-bearing steel. We rst patentannea such a rod (and by the term rod" we include the larger wires which may have been produced from the original rod by not over one or two passages through wire-drawing dies); by heating it to a temperature above the critical range, .and then quenching it throughv the critical range in a molten-material bath (as of molten lead or molten salt) having a temperature between 700 and 935 F. The patent-annealed rod, after suitable pickling and other preparation for wire-drawing, is then drawn to a wire of the desired size or substantially the desired size.`

This drawing usually produces a rather high tensile strength, perhaps of the order of 150,000 to 200,000 pounds per square inch; but this high tensile strength is accompanied by an undesirably` low elongation, of the order of about 1% to 2% (measured in 10-inch lengths). The wire in this condition has undesirably low ductility for a conductor of an overhead electric transmission line.

To increase that ductility, and at the same time to increase that elongation, to desirable values, we now carefully process-temper the wire. To that end we carefully heat that wire to a selected temperature, which is well below the critical temperature. That selected temperature may vary somewhat, as with theanalysis of the wire, being higher (otherthings being equal) for increased carbon content; andv it mayalso vary according to the tensile strength and the elongation desired, being higher for greaterelongation and less tensile strength. That temperature is between 825 and 1075 F. It is obtained most conveniently by passing the wire through a molten-lead or molten-salt bath of the desired temperature. -After the wire has reached this selected temperature, it is then allowed to cool, as by being passed through the air; and is then desir'ably passed through various baths in prepa` ration for zinc-coating, usually including a pickling bath, one or more water-washing baths, and a uxing bath.

Then, after being dried, the wire is through a molten-zinc bath of relatively low temperature, of the order of 825 to 900 F., in

which bath the wire takes on a hot-dip zinc.

v The hot-rolled wire rod of the desired analysis, outlined above, is obtained from a rollingmill.

This requires special heats of steel to get that desired analysis-selected between 0.25% and 0.85% carbon, between zero and 0.30% manpassed ganese, at least 0.05% combined silicon and phosphorus but not above 0.25% and desirably not above 0.15% silicon and not above 0.12% phosphorus, suitably little sulfur, and if desired some copper.

A coil of rod, after some preliminary drawing if desired, is put on a supply reel I0, from which the rod Il passes through a heating furnace I2, suitably heated so that the rod is raised to a temperature above the critical temperature range. From the heating furnace, the rod II is passed directly into a molten-material bath I3 (as of molten lead or molten salt) in which the temperature of the molten material is maintained at the desired temperature-between '100 and 935 F. From the molten-material bath I3, the rod II, after passing if desired over reverse rollers I4 to remove scale, passes to a tale-up block or reel I5.

'I'he patent-annealed rod II is then removed from the take-up block I5, suitably cleaned and e otherwise prepared for drawing, and put on a supply reel I6; from which it is fed through wiredrawing dies I1, in which the rod II is drawn to a wire I8. The wire is pulled through the dies I1 by a take-up block I9, on which the drawn wire is coiled. If there are a large number of wire-drawing dies I1, as there may bev` when the wire I8 is drawn to small diameter from a large rod, it may be desirable to do the wiredrawing in several steps; and even to repeat the patent-annealing at an intermediate stage in the drawing of the wire, with the quenching temperatures as set forth above, as in the apparatus shown in Fig. 1.

When the wire I8 has been drawn to the proper size, it is removed from the take-up block I9 and lower part thereof. .The molten lead or molten salt in the bath 2| is a temperature-raising liquid, as distinguished from thetemperature-lowering liquid of the lead or salt of the bath I3.

The wire I8 before it is passed intothe moltenmaterial bath 2| has a very high tensile strength, but its elongation and itsA ductility are too low. In the molten-material bath 2I there is a tempering action that is very carefully controlled, both by the temperature'of the molten material and by the duration of immersion of the wire in such molten material, to increase the ductility and the elongation to desired values without lowering the tensile strength too greatly. 'I'he duration of immersion, in continuous process, is controlled by the length of the molten-material bath and by the speed of the wire through the bath. By careful selection of the temperatures within the range indicated, it is possible to keep the tensile strength above 120,000 pounds per square inch, and in most cases above 135,000 pounds per square inch, and yet to increase the elongation to a final value of the order of 4% to 8%. With such tensile-strength and elongation values, the wire is eminently suitable for use as an alternating-current conductor in an overhead electric transmission line.

After passing through the molten-material bath 2|, the wire I8 is passed through the air to cool it, and then may be passed successively through various baths in preparation for hotdip zinc-coating. Such preparatory baths may include a pickling bath 22, a washing bath 23 containing washing water, and a fluxing bath 24 containing a suitable fluxing liquid (such as ammonium chloride); after which it is desirably passed over a drying plate 25, and thence into a molten-zinc bath 26 in which it takes on a coating of zinc. The temperature of the molten zinc is of the order of 825 to 900 F., and desirably between 840 and 860 F. The zinc coating taken onin the molten-zinc bath 26 is an adherent zinc coating, for we have found that such adherence is effectively obtained with the steel composition specified above. From the molten-zinc bath 26, the wire may pass if desired through another wire-drawing die 21, although this is frequently omitted. Whether or not there is this additional Wire-drawing die 21, the wire I8 finally passes to a take-up block 28, which furnishes the power for pulling the wire through all the apparatus .shown in Fig. 3.

The operation of patent-annealing described above serves a double useful purpose; first, it imparts to a steel rod a sorbitic structure which increases the toughness of the rod and its ability to withstand shock; second, it lowers the magnetic permeability of the rod when traversed by electric currents, and this in turn lowers the skin effect with alternating currents and so lowers the effective alternating-current resistance and reactance of the finished conductor. The operation of process-tempering in molten material,

after drawing, at a temperature between 825 and 1075 F., tempers the extreme hardness produced by the cold-working involved in that drawing, and imparts the ductility and elongation desirable for an electrical conductor used in overhead spans 0f an outdoor transmission line. This process-tempering, in order to accomplish our desired purpose, must avoid both too much annealing as well as too little annealing; because in the former case the conductor woul-d have inadequate tensile strength, and in the latter case it would have too little ductility and elongation. We accomplish this desired result by the control of the temperature limits in the process-tempering bath, as above described.

We claim as our invention:

1. A carbon-steel alternating-current conductor having rlowered magnetic permeability and lowered skin effect, resulting in lowered effective alternating-current .resistance and reactance, which conductor has an adherent hot-galvanized zinc coating and is made of hypo-eutectoid steel containing at least 0.25% of carbon, not in excess4 of 0.30% of manganese, and enough silicon and phosphorus to make a combined total of at least 0.05% but with silicon not in excess of 0.25% and phosphorus not in excess of 0.12%, and which has a sorbitic structure, and which has been subjected to cold-working and to subsequent partial annealing by which the effects of the cold-working have been partially but only partially eliminated so that effects of that coldworking in part persist, and which has' a tensile strength above 120,000 pounds per square inch and an elongation of the order of 4% to 8%.

2. A carbon-steel alternating-current conductor having lowered magnetic permeability and lowered skin effect, resulting in lowered efcess of 0.12%, and which has persisting in its grain structure mechanical and electrical-resistance and electrical-reactance effects produced' (a) by quenching through'the critical range in a bath of molten material having a temperature between 700 and 935 F., (b) by cold-working, and (c) by subsequent partial-annealing.

3. A carbon-steel alternating-current conductor having lowered magnetic permeability and lowered skin eiect, resulting in lowered effective alternating-current resistancel and reactance, which conductor has an adherent hot-galvanized zinc coating and is made of hypo-eutectoid steel containing at least 0.25% of carbon, not in excess of 0.30% of manganese, and enough silicon and phosphorus to make a combined total of at least 0.05% `but with silicon not in excess of 0.25% and phosphorus not in excess of 0.12%, and which has a sorbitic structure, and which has a tensile strength above 120,000 pounds per square inch and an elongation of the .order of 4% to 8%.

4. A carbon-steel alternating-current conductor having lowered magnetic permeability and lowered skin effect, resulting in lowered effective alternating-current resistance and reactance, which conductor has an adherent hot-galtoid steel containing at least 0.25% of carbon,

not in excess of 0.30% of manganese, and enough silicon and phosphorus to make a combined total of at least 0.05% but with silicon not in excess of 0.25% and phosphorus not in excess of 0.12%, and which has persisting in its grain structure mechanical and electrical-resistance and elec trical-reactance eiects produced by quenching through the critical range in a bath of molten material having a temperature between '700 and 935 F., and which has been subjected to coldworking and to subsequent partial annealing by which the effects of the cold-working have been partially but only partially eliminated so that eiects of thatcold-working in part persist, and which has a tensile strength of above 120,000 pounds per square inch.

5. A carbon-steel alternating-current conductor having lowered magnetic permeability and l lowered skin eiect, resulting in lowered effective alternating-current resistance and reactance, which conductor has an adherent hot-galvanized zinc coating and is made of hypo-eutectoid steel containing at least 0.25% of carbon, not in excess of 0.30% of manganese, and enough silicon and phosphorus to make a combined total of at least 0.05% but with silicon not in excess of 0.25% and phosphorus not in excess of 0.12%, and

` which has a sorbitic structure, and which has been subjected to cold-working and to subsequent partial annealing by which the effects of the cold-workingzhave been partially but only partially eliminated so that eiects of that coldworking in part persist.

FRANK F. FOWLE. FREDERICK M. CRAPO. 

